How to display database text box values shown on message box

const string sql = "SELECT * FROM MyTable";
var dataTable = new DataTable("MyTable");
using (var sqlConnection = new SqlConnection("MyConnectionStringBlaBlaBla"))
{
  sqlConnection.Open();
  using (var sqlDataAdapter = new SqlDataAdapter(sql, sqlConnection))
  {
    sqlDataAdapter.Fill(dataTable);
  }
}
MessageBox.Show(dataTable.Rows[0].ItemArray[0].ToString());